High efficiency fuel injection system for gas appliances

ABSTRACT

A unique control system is provided for fuel injection gas appliances to achieve efficient combustion by controlling the proportion of fuel and air variables. The combustion control system provides active feedback control of the combustion event and includes at least one detection sensor e.g. CO 2  CO sensor and O 2 , to trigger the modulation of a gas valve to adjust pressure and gas flow to the combustion chamber of a gas appliance. A processor receives the concentration signal from the detection sensor to generate a proportionate control signal to modulate a pressure regulator of the gas valve thereby to control future combustion events to achieve maximum fuel combustion efficiency. Accordingly, the injection system varies the proportion of air to fuel inflow to a prescribed optimum range achieving efficient fuel combustion.

BACKGROUND OF THE INVENTION

The present invention relates to an improved method and apparatus forfuel injection for gas appliances.

Gas appliances such as heaters serve as floor heaters, space heaters,room heaters, central furnaces, clothes dryers and cooking ranges.Existing gas heating appliances typically employ manually operated gasvalves to regulate and control gas flow to burners for combustion togenerate heat from the burning of natural or propane gas.

The fixed orifice in a conventional gas valve, however, is not capableof active adjustment of pressure and flow rate of gas into the burnerresulting in inefficient combustion i.e. too little heat and too muchexhaust generated from a gas-heating appliance.

Excessive gas flow with inadequate air in the combustion mixture, orvise versa, will cause less heat and excess exhaust. Moreover, variousambient conditions such as altitudes in different parts of the world,are variable factors that can contribute to combustion efficiency. Thecomponents of conventional gas heating appliances are generally fixedand not self-adjusting to account for these various ambient conditions.

Those skilled in the art have recognized a significant need for avariety of control systems that utilizes the concentration of carbondioxide.

U.S. Pat. No. 6,398,118 issued to Rosen, et al., discloses a system formonitoring and modifying the quality and temperature of air within aconditioned space including a blower unit, a damper unit for selectivelyadmitting outside air into the conditioned space, a temperaturemoderating unit and a control unit.

The Rosen system relates to the art of conditioning indoor living andworking and other enclosed public spaces. More particularly, the patentdiscloses a system in which the carbon dioxide (CO₂) level is monitoredand controlled by apparatus in which the CO₂ sensor and supportcircuitry is integral with a thermostat which also serves toconventionally control the temperature range within the conditionedspace.

The principle of operation of the CO₂ sensor is stated to be that, thecell constituting the cathode, anode and solid electrolyte, becomessusceptible to readily measurable change in accordance with the CO₂concentration at the cell. This known effect appears to be due to achemical reaction between the CO₂ and the electrolyte which must beselected to enhance the extent of the change in accordance with the gasof interest. Combinations of electrodes and electrolytes suitable forthe purpose are discussed, for example, by S. Azad, S. A. Akbar, S. G.Mhaisalkar, L. D. Birkefeld and K. S. Goto in the Journal of theElectrochemical Society, 139, 3690 (1992). One suitable combinationwhich gives very good results for measuring CO₂ concentration is:platinum (Pt) for the cathode, reference electrode 30; silver (Ag) forthe anode, sensing electrode 31; and a mixture of Na₂ CO₃, BaCO₃ and AG₂SO₄ as the solid electrolyte.

U.S. Pat. No. 6,286,482 issued to Flynn, et al., discloses a premixedcharge compression ignition engine, and a control system, whicheffectively initiates combustion by compression ignition and maintainsstable combustion while achieving extremely low oxides of nitrogenemissions, good overall efficiency and acceptable combustion noise andcylinder pressures. The Flynn engine and control system effectivelycontrols the combustion history, that is, the time at which combustionoccurs, the rate of combustion, the duration of combustion and/or thecompleteness of combustion, by controlling the operation of certaincontrol variables providing temperature control, pressure control,control of the mixture's autoignition properties and equivalence rationcontrol. The combustion control system provides active feedback controlof the combustion event and includes a sensor, e.g. pressure sensor, fordetecting an engine operating condition indicative of the combustionhistory, e.g. the start of combustion, and generating an associatedengine operating condition signal. A processor receives the signal andgenerates control signals based on the engine operating condition signalfor controlling various engine components to control the temperature,pressure, equivalence ration and backlash or autoignition properties soas to variably control the combustion history of future combustionevents to achieve stable, low emission combustion in each cylinder andcombustion balancing between the cylinders.

The Flynn patent discloses a strategy for controlling the start anddirection of combustion by varying the air/fuel mixture autoignitionproperties. The autoignition properties of the air/fuel mixture may becontrolled by injecting gas, e.g. air, oxygen, nitrogen, ozone, carbondioxide, exhaust gas, etc., into the air or air/fuel mixture either inthe intake system.

U.S. Pat. No. 6,392,536 issued to Tice, et al. discloses amulti-function detector which has at least two different sensors coupledto a control circuit. In a normal operating mode the control circuit,which would include a programmed processor, processes outputs from bothsensors to evaluate if a predetermined condition is present in theenvironment adjacent to the detector. In this mode the detector exhibitsa predetermined sensitivity. In response to a failure of one of thesensors, the control circuit processes the output of the remainingoperational sensor or sensors so that the detector will continue toevaluate the condition of the environment with substantially the samesensitivity.

U.S. Pat. No. 5,644,068 issued to Okamoto, et al. discloses a gas sensorof the thermal conductivity type suitable for the quantitative analysisof the fuel vapor content of a fuel-air mixture. The Okamoto gas sensorcomprises a sensing element and a compensating element , each of whichincludes an electrically-heated hot member incorporated into aWheatstone bridge circuit powered by a constant current supply circuit.The constant current supply circuit is adjusted and regulated such thatthe hot member of the sensing element is heated with an electric currentof such an intensity that corresponds to a point of transition (Y) atwhich, at the interface of the hot member and the mixture, thepredominant mode of heat transfer changes from thermal conduction tonatural convection.

The dislosures of the foregoing patents are hereby incorporated by thisreference.

While recognizing the advantages of control systems utilizing carbondioxide as possible parameter, these systems do not strive to achievecombustion efficiency through the recognition of carbon dioxide, carbonmonoxide and oxygen gas concentration as a critical factors for activefeedback control. The present invention achieves these goals.

SUMMARY OF THE INVENTION

The present invention relates to an improved method and apparatus forfuel injection for gas appliances.

A unique control system is provided for fuel injection gas appliances toachieve efficient combustion by controlling the proportion of fuel andair variables. The combustion control system provides active feedbackcontrol of the combustion event and preferably includes a CO₂ CO sensorand O₂ to trigger the modulation of a valve to adjust pressure and gasflow to combustion chamber of gas appliance. A processor receives theconcentration signals from the sensors and generates control signalsbased on the concentration signal for controlling a pressure regulatorof the gas valve so as to variably control future combustion events toachieve maximum fuel combustion efficiency. Accordingly, the controlsignal varies the proportion of air to fuel inflow to a prescribedoptimum range achieving efficient fuel combustion.

The present invention achieves improved combustion efficiency byadjustment of pressure and fuel flow related to changing ambientconditions. One embodied system comprises a CO₂ sensor to measure theconcentration of carbon dioxide out of combustion chamber of a gasheating appliance and relay the signal to an electronic circuitry; afterreceiving the signal, the electronic circuitry will activate a device toadjust pressure regulator of a gas valve to a prescribed optimum range.

In one embodied form, the present invention provides an improved methodand apparatus for achieving high efficiency of combustion by comprisingactive feedback control means based upon detection of the concentrationof carbon dioxide. Assuming fixed exhaust gas flow from combustion, ifthe concentration level of carbon dioxide exceeds about nine percent(9%), the control means will accordingly decrease the air flow into theburner of the gas heating appliance. If the concentration of carbondioxide in the exhaust gas is less than seven percent (7%), the controlmeans will proportionately increase the intake air flow to thecombustion chamber. Thus greatest combustion efficiency can be achievedby monitoring and maintaining the concentration of carbon dioxide withina range of between about 7 to 9 percent.

In a second embodiment, the inventive system comprised a CO₂ sensor, COsensor, O₂ sensor to trigger the modulation of gas valve to adjustpressure of gas pressure and gas flow to combustion chamber of gasappliance. In operation, modulation will take place in a range ofconcentration. For instance, in the case of CO₂, modulation is withinthe range of 7 percent to 9 percent. Gas pressure and flow will beadjusted in responding to changes of concentration, way before CO₂reaches 7 percent or 9 percent. Actually, modulation of gas value can beto such an extent of virtually shutting down gas flow to a halt.

The inventive system comprises a processor that receives the qualitativeand quantative signal from the carbon dioxide sensor and providesfeedback control to an electronic control unit (ECU). ECU receives thesensor signal and processes the signal to determine the appropriateadjustment, if any, to the flow of air to be mixed with fuel forcombustion in the burner unit. The signal reflecting the carbon dioxideconcentration in the exhaust gas is then compared to a predetermineddatabase of desired airflow adjustment values. Based on the comparisonof the actual airflow to the desired airflow adjustment value, the ECUthen generates a plurality of output signals, for variably controlling apressure regulator of a gas intake flow valve and other respectivecomponents of the system so as to effectively ensure, that the futurecarbon dioxide concentration in the exhaust gas is maintained within theprescribed optimum range.

The combustion control scheme is most preferably implemented in softwarecontained in ECU that includes a central processing unit such as amicro-controller, micro-processor, or other suitable micro-computingunit. Accordingly, the unique system achieves high efficiency combustionin a wide variety of gas heating appliances.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional side view of one embodied CO₂ sensor andPitot tube in accordance with the present invention.

FIG. 2 is a side sectional view illustrating the system components andplacement of a CO₂ sensor in the control processor in accordance withthe present invention.

FIG. 3 is a schematic sectional view depicting a gas valve in accordancewith one embodied form of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A unique control system os provided for fuel injection heatingappliances to achieve efficient combustion by controlling the proportionof fuel and air variables. The combustion control system provides activefeedback control of the combustion event and includes a CO₂ CO sensorand O₂ to trigger the modulation of a gas valve to adjust pressure ofgas pressure and gas flow to combustion chamber of gas appliance. Aprocessor receives the concentration signals from the sensors andgenerates control signals based on the concentration signal forcontrolling a pressure regulator of the gas valve so as to variablycontrol future combustion events to achieve maximum fuel combustionefficiency. Accordingly, the control signal varies the proportion of airto fuel inflow to a prescribed optimum range achieving efficient fuelcombustion.

In one embodied form, the present invention provides an improved methodand apparatus for achieving high efficiency of combustion by comprisingactive feedback control means based upon detection of the concentrationof carbon dioxide. Assuming fixed exhaust gas flow from combustion, ifthe concentration level of carbon dioxide exceeds about nine percent(9%), the control means will accordingly decrease the air flow into theburner of the gas heating appliance. If the concentration of carbondioxide in the exhaust gas is less than seven percent (7%), the controlmeans will proportionately increase the intake air flow to thecombustion chamber. Thus greatest combustion efficiency can be achievedby monitoring and maintaining the concentration of carbon dioxide withina range of between about 7 to 9 percent.

In a second embodiment, the inventive system comprised a CO₂ sensor, COsensor, O₂ sensor to trigger the modulation of gas valve to adjustpressure of gas pressure and gas flow to combustion chamber of gasappliance. In operation, modulation will take place in a range ofconcentration. For instance, in the case of CO₂, modulation is withinthe range of 7 percent to 9 percent. Gas pressure and flow will beadjusted in responding to changes of concentration, way before CO₂reaches 7 percent or 9 percent. Actually, modulation of gas value can beto such an extent of virtually shutting down gas flow to a halt.

The sensor module provides a 0-4 VDC output scaled to 0-2000 ppm CO₂.The sampling method for detection of the carbon dioxide concentrationmay be either flow through or diffusion and can be configured to measureppm levels up to 5%. The modules include self-calibration algorithm thateliminates the need for on-going calibrations.

The CO sensor is operational to trigger the modulation of gas valve tolower the amount of gas flow to combustion chamber of gas appliance. Ifthe concentration is less than 65 PPM, the sensor is not activated.Preferably, the CO sensor accumulates concentration up to 65 PPM ofcarbon monoxide in one hour.

The O₂ sensor is operational to trigger the modulation of gas valve tolower the amount of gas flow to combustion chamber of gas appliance. Ifthe level is over 19.5 percent, the sensor is not activated.

The system may use conventional shut off mechanisms for instancedisclosed in U.S. Pat. No. 5,838,243, which is hereby incorporated bythis reference.

After generating the sensor concentration signal, the control processorwill determine the desired adjustment of air inflow by setting thepressure regulator of a gas valve to a prescribed optimum range.

In this respect the CO₂ Sensor module communicates over an asynchronous,UART interface at 9600 baud, no parity, 8 data bits, and 1 stop bit.When the host computer of PC communicates with the sensor, the hostcomputer sends a request to the sensor, and the sensor returns aresponse. The host computer acts as a master, initiating allcommunications, and the sensor acts as a slave, responding with a reply.

Preferably, sensor commands and replies are wrapped in a securecommunications protocol to insure the integrity and reliability of thedata exchange. One suitable communications protocol for the serialinterface and the command set for the module CO₂ Sensor are set forthbelow.

Each command to the sensor consists of a length byte, a command byte,and any additional data required by the command. Each response from thesensor consists of a length byte and the response data if any. Both thecommand to the sensor and the response from the sensor are wrapped in acommunications protocol layer.

-   -   Command: <length><command>additional_data>    -   Response: <length><response_data>

The communications protocol consists of two flag bytes (0xFF) and anaddress byte as a header, and a two-byte CRC as a trailer. In addition,if the byte 0xFF occurs anywhere in the message body or CRC trailer, theprotocol inserts a null (0x00) byte immediately following the 0xFF byte.The inserted 0x00 byte is for transmission purposes only, and is notincluded in the determination of the message length or the calculationof the CRC.

-   -   Header Message Body Trailer    -   <flag><flag><address><Command/Response><crc_Isb><crc_msb>

When receiving a command or response, the flags and any inserted 0x00bytes must be stripped from the message before calculating theverification CRC. A verification CRC should be computed on all receivedmessages from the sensor and compared with the CRC in the messagetrailer. If the verification CRC matches the trailer CRC, then the datafrom the sensor was transmitted correctly with a high degree ofcertainty.

In response to the concentration signal from the sensor module the airflow from a gas valve will be adjusted by pressure regulator before itflows to burner, prior to combustion chamber. If concentration of carbondioxide is more than 9 percent (9%), gas flow will be adjusted upward toincrease its mixture with air; and if concentration of carbon dioxide isless than 7 percent (7%), gas flow will be adjusted downward to decreaseits mixture with air.

In the CO₂ module, a bus interfaces to both an external processor andthe A/D converter which is collecting the CO₂ data. When the module iscollecting data, its serial shift clock is configured to generate itsown internal clock. That is, the module is said to be operating in“master” mode. When the CO₂ module is communicating with an externalprocessor, it relies upon the external processor to supply the clockpulse, called the “slave” mode.

Thus, to an external process, the CO₂ module appears as a slave on thebus. The external processor is the master, meaning that it provides theSK clock signal for both sending and receiving data across the bus. Fromthe CO₂ module's point of view, during communications with an externalprocessor, is SI (serial in) and SK (serial clock) are inputs, and itsSO (serial out) is an output. Additionally, there are two digitalhandshake lines that an external processor uses to communicate with theCO₂ module.

Every data exchange between an external processor and the CO₂ modulestarts with the external processor sending a request data-packet—severalbytes—to the CO₂ module. The CO₂ module then responds by returning aresponse data-packet to the external processor. The request data packetcontains a command byte, and perhaps one or more parameter bytes.

After receiving each byte in a request data packet, the CO₂ moduleraises the UB_ACK handshaking line. When it is ready to receive the nextbyte it lowers UB_ACK. The external processor must send the next byte tothe CO₂ module within 10 milliseconds from the time the UB_ACK line goeslow. This handshaking between bytes provides flow control and insuresthat the external processor does not overrun the CO₂ module's inputbuffer and that the CO₂ module does not wait indefinitely for theexternal processor to send the next byte. After receiving the final byteof the request data-packet, the CO₂ module again raises UB_ACK.

When the CO₂ module has processed the request and is ready to send thefirst byte of the response data-packet, the CO₂ module lowers UB_ACK.The external processor has 10 milliseconds from the time the UB_ACKlines goes low in order to start the clock and receive the byte. Aftertransmitting the byte, the CO₂ module raises UB_ACK, and lowers it againwhen it is ready to transmit the next byte. The process continues untilall bytes of the response data-packet have been transmitted to theexternal processor. The 10 millisecond time limit insures that the CO₂module does not wait indefinitely for the external processor to startthe clock to receive the byte.

After sending the final byte in a response, the CO₂ module raises UB_ACKand leave it high. The external processor then raises UB_REQ, concludingthe data interchange. UB_REQ must stay high longer than a specifiedminimum before the external processor lowers it to start the next dataexchange.

At the conclusion of a response data packet, the CO₂ module will waitapproximately 100 milliseconds after the final UB_ACK goes high beforeinitiating its return to master mode and the resuming of datacollection. If the external processor raises and lowers UB_REQ duringthis delay interval, the module stays in slave mode and immediatelyservices the new request. The delay interval gives the externalprocessor the opportunity to send a series of commands in rapidsuccession to the module. Note that the CO₂ module is not functioning asa sensor while it is in the slave mode.

The raising of UB_REQ, together with the expiration of the delay timeinterval, is the signal to the CO₂ module to return to Microwire mastermode and resume its A/D converter data collection. Microwire modeconversion and re-initialization for data collection is a time consumingprocess, and the module has only three opportunities during the processto abort and respond to a new UB_REQ. Hence, for non-PPM/Temperaturerequest, it is most time-efficient to start the next UB_REQ during thedelay interval following the previous request.

If the external processor needs to terminate an incomplete data exchangeit raises the UB_REQ line. When the CO₂ module see this, it discards thecontents of its communication buffers and then respond by raising theUB_ACK.

If the CO₂ module needs to terminate an incomplete data exchange, itraise UB_ACK. If UB_ACK remains high longer than the maximum timespecified for UB_ACK High Between Bytes, then the external processormust recognize this as termination of an incomplete data exchange. Forexample, if the CO₂ module receives bytes that do not correspond to avalid request data-packet then it raises UB_ACK and holds it high,signaling termination of an incomplete data exchange.

The CO₂ module starts a 10 millisecond timeout timer each time it lowersUB_ACK. The external processor must respond by starting the serial shiftclock within this interval so that the module can transmit or receivethe pending byte. If the external processor fails to start the clock,the CO₂ module presumes that the communication has been aborted and willraise UB_ACK.

If either the external processor or the CO₂ module terminates a dataexchange, no new communication can be initiated until both UB_ACK andUB_REQ have return to the high state. The new command then starts withthe external processor lowering UB_REQ as described above.

The inventive system comprises a processor that receives the qualitativeand quantitave signal from the carbon dioxide sensor and providesfeedback control to an electronic control unit (ECU). ECU receives thesensor signal and processes the signal to determine the appropriateadjustment, if any, to the flow of air to be mixed with fuel forcombustion in the burner unit. The signal reflecting the carbon dioxideconcentration in the exhaust gas is then compared to a predetermineddatabase of desired airflow adjustment values. Based on the comparisonof the actual airflow to the desired airflow adjustment value, the ECUthen generates a plurality of output signals, for variably controlling apressure regulator of a gas intake flow valve and other respectivecomponents of the system so as to effectively ensure, that the futurecarbon dioxide concentration in the exhaust gas is maintained within theprescribed optimum range.

The combustion control scheme is most preferably implemented in softwarecontained in ECU that includes a central processing unit such as amicro-controller, micro-processor, or other suitable micro-computingunit. Accordingly, the unique system achieves high efficiency combustionin a wide variety of gas heating appliances.

1. A high efficiency fuel injection system for gas appliances, thesystem comprising in combination: a) means for qualitative andquantitative sampling of combustion exhaust gas from a appliance; b)sensor means for detecting the concentration of a component selectedfrom the group consisting of carbon dioxide, carbon monoxide and/oroxygen and combinations thereof present in the combustion exhaust gas;c) means converting the detected concentration of said component to adigital value signal for relay to a central processor unit; d) means forcomparing the carbon dioxide concentration value signal with a storeddesired concentration value; e) means for continuously entering thedigital value signal into a computer and comparing the value signal withthe desired concentration value; f) means for converting the digitizedvalues to calibrated values; g) means for calculating the desired airflow for optimum combustion efficiency from the calibrated value; h)means for directing the signal derived from the computer to a regulatorvalve for adjusting the concentration of fuel and air for futurecombustion.